Archive for Sunday, June 9, 2002

Timing counts in controlling bagworms

June 9, 2002


In the gardening world, timing means everything.

For example, you have to apply crabgrass preventer in the spring before weeds emerge, and spray for peach leaf curl before it damages your peach trees.

As the warm days of spring encourage the flowers, trees and shrubs to grow, they also are encouraging bagworms to emerge and begin feeding. Now is the time to begin your bagworm control program  before these perennial pests cause major damage this summer.

Bagworms overwinter as eggs in the bags left from last year's female worms. Young larvae normally hatch and emerge mid- to late May in Lawrence. However, in some years they may not emerge until mid-June.

With such variation in hatch time, it is best if you check for live bagworms before spraying your landscape. Recently hatched bagworms are light green and the same size and shape as a pencil lead. They grow rapidly and produce miniature versions of the adult bags.

If you spot young bagworms on evergreen trees and shrubs, start treating for them in the next few weeks. This should be enough time for most of the worms to emerge, yet they will still be small and not hard to kill.

A number of contact insecticides are labeled for bagworm control in the home landscape. Some of the more common chemicals are acephate, bifenthrin, carbaryl (Sevin), cyfluthrin, diazinon, dimethoate, malathion, permethrin and spinosad.

Given that many companies use the same active ingredients to manufacture their own products, homeowners should visit retail outlets to see what products they carry.

If you are interested in using an organic control, choose products containing Bacillus thuringiensis. This natural toxin is effective if used on larvae while they are small. The key to success with any of these products is to thoroughly cover the upper and lower leaf surface, as well as all the branches and trunks of infested plants.

Bagworms have been around as long as we have been growing evergreen trees and shrubs in the landscape. With little known benefit to society, their claim to fame is the damage they cause by eating foliage from a wide variety of plants. When it comes to controlling bagworms, the best line of defense is a good offense. Scout for the young larvae now. If found, treat with an approved insecticide. Then, re-inspect in seven to 10 days and treat again if needed.

 Bruce Chladny is horticulture agent at K-State Research and Extension-Douglas County. For more information, call him at 843-7058 from 8 a.m. to 5 p.m. weekdays.

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